The present invention relates to an abnormality diagnosis device for a positive crankcase ventilation apparatus, which includes a PCV passage for supplying blow-by gas to an intake passage and a PCV valve for regulating the flow rate of the blow-by gas in the PCV passage.
A positive crankcase ventilation apparatus for an internal combustion engine includes a PCV passage through which blow-by gas is drawn from a crankcase to an intake passage and a PCV valve for regulating the flow rate of the blow-by gas in the PCV passage.
In the positive crankcase ventilation apparatus, the occurrence of an abnormality, such as the deposition of sludge along the PCV passage or jamming of the PCV valve, may cause difficulties for properly ventilating the interior of the crankcase. In order to solve this problem, a diagnosis must be performed to determine the occurrence of such an abnormality.
Japanese Laid-Open Patent Publication No. 5-163993 describes an abnormality diagnosis device that compares an air-fuel ratio feedback correction coefficient taken when forcibly closing the opening of the PCV valve and the air-fuel ratio feedback correction coefficient taken when forcibly opening the opening of the PCV valve by an amount that is the same as that during normal driving. Based on the comparison, the abnormality diagnosis device determines whether or not an abnormality is occurring in the positive crankcase ventilation apparatus.
In the abnormality diagnosis device described in Japanese Laid-Open Patent Publication No. 5-163993, when forcibly opening the PCV valve in a state in which the blow-by gas in the crankcase contains a large amount of fuel components, the large amount of fuel components is supplied to the intake passage through the PCV valve. This may result in excessive enrichment of the air-fuel ratio. Specifically, although the abnormality diagnosis device described in Japanese Laid-Open Patent Publication No. 5-163993 allows for determination of an abnormality in the positive crankcase ventilation apparatus, the PCV valve is controlled during the abnormality diagnosis such that the air-fuel ratio becomes excessively enriched.